1961. These investigators irradiated the spleens and bone marrows of mice, rendering them acellular, and then injected them with bone marrow cells. Within days, colonies appeared on the spleens of the mice and were referred to as colony-forming units-spleen (CFU-S), with cells capable of regenerating into mature hematopoietic cells. In present-day terminology, CFU-S are the pluripotential stem cells (Fig. 2.3). Multipotential stem cells are capable of differentiation into non-lymphoid or lymphoid precursor committed cells.7 Nonlymphoid committed cells will develop into the entire white cell, red cell, or megakaryocytic family (CFU-GEMM). The lymphocytic committed cell (LSC) will develop into T cells or B cells, which are of different origins. T cells are responsible for cellular immunity (cell-to-cell communication), whereas B cells are responsible for humoral immunity, the production of circulating antibodies directed by plasma cells. Each of these committed cells evolves into their adult form

Figure 2.2 Internal structure of the bone marrow.

through proliferation, differentiation, and maturation. Chemical signals such as cytokines and interleukins are uniquely responsible for promoting a specific lineage of cell. Most of these substances are glycoproteins that will target specific cell stages. They control replication, clonal or lineage selection and are responsible for maturation rate and growth inhibition of stem cells.8 Many cytokines are available as pharmaceutical products. Recombinant technology has made it possible to purify and produce cytokines such as EPO, granulocyte-colony stimulating factor (G-CSF), and granulocyte-macrophage colony-stimulating factor (GM-CSF). These products are used to stimulate a specific cell production to yield therapeutic benefit for the patient. Specific conditions in which recombinant cytokines have been useful are as follows9:

1. Recovery from neutropenia resulting from myelotoxic therapy

20 Part I • Basic Hematology Principles

2. Graft versus host disease after bone marrow transplant therapy

3. To increase white counts in patients with AIDS on antiretroviral therapy

An abbreviated list of cytokines and the cell lines they stimulate is included in Table 2.2.

Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

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